Trolley with tractor drive for use in curved enclosed tracks and system including the same

ABSTRACT

An enclosed track system comprising an enclosed track having at least one curve and a trolley for negotiating the curve. The trolley includes an externally located drive section and a rolling section having first and second roller portions located within the track. The first roller portion includes rollers for rolling on flange portions of the track. The second roller portion includes a driven wheel and a pair of support rollers. The driven wheel rolls on an inner surface of the top of the track. The pair of support rollers roll on flange portions of the track and are mounting on respective rods for pivoting action about vertical axes. The drive section includes a motor, a drive sprocket and associated chain for positively driving the driven wheel. The drive section also includes an articulated joint coupling the first and second roller portions together.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to overhead conveyor systems and more particularly to systems making use of an enclosed track in which a trolley is arranged to roll to support something from the trolley.

2. Description of Related Art

Enclosed track conveyor systems are commonly used to support and carry items from a wheeled trolley located within the interior of an enclosed track. As is known enclosed tracks are hollow members having a top-wall, a pair of sidewalls projecting downward from the top wall and a pair of marginal flanges extending horizontally from respective ones of the sidewalls. The flanges are spaced from each other to form a slot therebetween. The trolley is located within the interior of the track, with its wheels or rollers disposed on the interior (upper) surface of the flanges.

Examples of enclosed track systems including internally located trolleys for rolling down the interior of the track are found in U.S. Pat. No. 3,589,503 (Leach), U.S. Pat. No. 3 627,595 (Leach) and U.S. Pat. No. 6,450,326 (Hoffinan et al.). The trolleys of the foregoing patents are arranged so that they can negotiate curves in the track.

In some prior art systems, the movement or rolling of a trolley down the interior of an enclosed track is accomplished by using a tractor drive that is mounted on the trolley, but located outside of the track. Such tractor drives make use of a drive wheel, which extends through the slot in the track to frictionally engage the inner surface of the top wall of the track. The drive wheel is rotated by a motor mounted on the externally located tractor. This arrangement requires that the drive wheel be of a relatively large diameter. As a result such tractors are not suitable for use in systems wherein the enclosed track includes a relatively small radius curve, since the drive wheel would engage or bind in the slot. While some enclosed track systems make use of tractors having drive wheels that engage and ride on the bottom of the track, i.e., the inner surface of one or more of the flanges, such systems are not practical due to splices used on the track, which results in an uneven drive surface, and make it difficult to keep a constant pressure on the drive wheel.

In U.S. Pat. No. 6,718,885, which is assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed an enclosed track system that makes use of a drive system facilitating the driving of a trolley through a curve in an enclosed track. To that end, the system of that patent includes an enclosed track system comprising an enclosed track having at least one curved portion and a trolley. The track includes a slot extending along its length. The trolley includes a rolling section having first and second roller portions and an externally located drive section. The first and second roller portions are located within the track and spaced from each other. The second roller portion includes a pair of guide rollers disposed within the slot in the track and a passive or floating driven wheel located within the track. The driven wheel is arranged to be driven by frictional engagement of a driving wheel and is arranged to roll on an inner surface of the track to propel the trolley along the track. To the end the drive section includes a motor to cause the drive wheel to rotate, whereupon it causes the driven wheel to rotate so that the trolley rolls along the track. The drive section has an articulated joint coupling the first and second roller portions to each other, with the articulated joint enabling the first and second roller portions to pivot longitudinally with respect to each other so that the trolley can negotiate curves in the track. The articulated joint is in the form of a dual-hinged, articulated tow-arm assembly. That assembly basically comprises an elongated tow-arm member having a pair of brackets at its opposite ends. One bracket is secured via a hinged connection to a portion of the frame supporting the motor at the second roller portion, while the other bracket is secured via a hinged connection and an associated clevis to a portion of the first roller portion. The pivot point at the second roller portion is located forward of the longitudinal position of the guide rollers.

While the drive system of the '885 patent is suitable for its intended purposes, it leaves something to be desired from two standpoints. In particular, one is potential slippage of the driven wheel, since it is a floating member driven by frictional engagement from the driving wheel. The other is possible side loading torque resulting from the construction of the articulated joint coupling, and in particular the fact that the pivot axis for the second roller portion is located forwardly of the guide rollers and the point at which the driven roller engages the inner surface of the track. Such a side load torque could result in accelerated wear of the guide rollers.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a trolley for use with an enclosed track having at least one curved portion, the enclosed track being an elongated hollow member having a top wall portion, a pair of side wall portions and a pair of flanged portions, the flanged portions being spaced from each other to define a slot therebetween extending longitudinally along the track. The trolley comprises a rolling section and a drive section, with the rolling section having first and second roller portions. The first roller portion is located within the track and comprises at least one support roller arranged to roll on at least one of the flange portions of the track. The second roller portion comprises a driven wheel, a pair of support rollers and a pair of guide rollers mounted on respective vertically extending rods. Each of the guide rollers is located within the slot of the track, with the guide rollers being positioned immediately fore and aft of the position of the driven wheel. The pair of support rollers comprises an upstream support roller and a downstream support roller. The upstream support roller is located adjacent one side of the drive wheel and is mounted on the drive section for pivoting action about an upstream vertical axis. The downstream support roller is located adjacent a diametrically opposed side of the driven wheel and mounted on the drive section for pivoting action about a downstream vertical axis, whereupon the upstream and downstream support rollers are enabled to roll along at least one of the flange portions of the track while said driven wheel rolls along the top wall portion of the track in the center thereof. The drive section is located outside of the track.

In one preferred aspect of this invention the drive section includes a driving sprocket and an associated driving loop, e.g., a chain. The driving sprocket is arranged for positively engaging the driving loop. The driving loop is arranged for positively engaging the driven wheel to cause the driven wheel to rotate about a horizontal axis so that it rolls on the inner surface of the track to propel the trolley along the track.

In another preferred aspect of this invention the first roller portion of the trolley is coupled to the second roller portion by an articulated joint. The articulated joint comprises an elongated member having a first end portion and a second end portion. The first end portion is pivotably coupled to the first roller portion at a first vertically extending axis. The second end portion is pivotably coupled to the second roller portion at a second vertically extending axis. The second vertically extending axis is located approximately midway between the vertically extending rods for the guide rollers.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein:

FIG. 1 is an isometric view, partially in section, of a portion of an enclosed track system making use of one embodiment of a trolley constructed in accordance with this invention shown in the process of negotiating a curve in the enclosed track.

FIG. 2 is a side elevated view of the portion of the track and trolley shown in FIG. 1;

FIG. 3 is a sectional view of the track and trolley taken along line 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional view of the track and apportion of the trolley taken along line 4-4 of FIG. 2;

FIG. 5 is an enlarged sectional view of a portion of the track and trolley shown in FIG. 3.

FIG. 5A is a view similar to FIG. 5, showing more of the details of the construction of the components shown in FIG. 5;

FIG. 6 is a sectional view taken along line 6-6 of FIG. 2; and

FIG. 7 is a view similar to FIG. 3 but taken from the opposite direction.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 there is shown at 20 one exemplary embodiment of an enclosed track system constructed in accordance with this invention. The system 20 includes a conventional enclosed track 22 and a tractor-drive trolley 24. The details of the trolley 24 will be described later. Suffice it for now to state that the trolley 24 includes two internal roller sections 26 and 28 arranged to be located within the track 22, and an articulated externally located tow-arm assembly 30, The tow-arm assembly 30 is located outside of, i.e., below, the track 22 and is coupled to the both internal roller sections for moving the trolley along the track.

Turning now to FIGS. 1 and 5, the details of the track 22 will now be discussed. As can be seen the track is of the conventional “enclosed-type” construction. One particularly suitable enclosed track is that sold by SPANCO, a division of Transol Corporation, the assignee of the invention. The track 22 is an elongated member that can be linear or curved or both linear and curved, i.e., having at least one linear portion and at least one curved portion. In the exemplary system 20, the portion of the track 22 that is shown in FIG. 1 is curved. Other portions of the track 22 of the system 20 can be linear or curved, depending upon the application for the system. The track is formed of a strong material, e.g., steel, and has a horizontally disposed top wall 32, a pair of vertical sidewalls 34 and 36 projecting downward from the top wall 32, a pair of angularly located sidewalls 38 and 40 located below the vertical sidewalls 34 and 36, respectively, and a pair of horizontally disposed flanges 42 and 44 projecting inward from the ends of the angularly located sidewalls 38 and 40, respectively, to form a slot 46 also used for axles therebetween.

The track 22 is arranged to support at least one trolley 24 to enable the trolley to be driven, i.e., moved, along the track to any desired longitudinal position. The trolley 24 may be used to support or hold some other device or member from it. For example, the trolley 24 can be used to support a lifting device (not shown), such as a winch or hoist or one end of a bridge member to form a bridge crane.

Turning now to FIGS. 1 and 2 the details of the trolley 24 will now be discussed. As can be seen, the trolley 24, basically comprises the heretofore identified two internal roller sections 26 and 28 and the tow-arm assembly 30. The roller section 26 serves as the first or “front” roller section of the trolley 24 and includes two pairs of wheels or rollers located within the interior of the track 22. One pair of rollers is designated by the reference numbers 26A and 26B, while the other pair is designated by the reference numbers 26C and 26D. In accordance with one preferred embodiment of this invention the rollers are formed of a tough, wear-resistant material, such as polyamide, but can be formed of any other material used in conventional enclosed track trolleys. As best seen in FIG. 1 the rollers 26A and 26B are mounted on an axle 47 and the rollers 26C and 26D are mounted on an axle 48. The rollers are held in place on their associated axles by use of conventional snap-rings. The axles 47 and 48 are fixedly mounted on a roller support body 50, in the form of a weldment, so that the longitudinal axis of each axle extends perpendicularly to the plane of the roller support body 50 and to the longitudinal axis of the track 22. The axles 47 and 48 are spaced from each other longitudinally. The rollers 26A-26D are arranged so that the periphery of each roller engages and rolls along the interior surface of a respective flange 42 or 44 of the track 22. In particular, the rollers 26A and 26C are arranged to engage and roll on the inner surface of the flange 42 of the track 22, while the rollers 26B and 26D are arranged to engage and roll on the inner surface of the flange 44 of the track 22. The roller support body 50 also includes a downwardly depending plate-like portion 52 which extends through the slot 46 in the track. The plate-like portion 52 is pivotably coupled to a portion of the tow-arm assembly 30 (to be described later).

The roller section 28 serves as the second or “rear” roller section of the trolley 24 and also includes two pairs of wheels or rollers located within the interior of the track 22. One pair of rollers is designated by the reference numbers 28A and 28B, while the other pair is designated by the reference numbers 28C and 28D. The rollers 28A-28D are of similar construction to the rollers 26A-26D, but are smaller in diameter, for reasons to become apparent later. The rollers 28A and 28B are mounted on an axle 54 and the roller pair 26C and 26D are mounted on an axle 56. The axle 54 is mounted on a roller support body 58 (FIG. 2). The roller support body 58 is in the form of a plate-like member. That member is mounted on a spring-biased rod (to be described later) forming another portion of the externally located tractor drive 24. A portion of the roller support body 58 extends through the slot 46 in the track 22. The axle 54 is mounted perpendicularly to the roller support body 58. The rollers 28A and 28B are dimensioned so that their peripheries engage and roll along the interior surface of flanges 42 or 44, respectively, of the track 22. The axle 56 is mounted on an identical roller support body 60. That member is mounted on a spring-biased rod (to be described later) forming another portion of the externally located tractor drive 24. A portion of the roller support body 60 extends through the slot 46 in the track 22. The rollers 28C and 28D are dimensioned so that their peripheries engage and roll along the interior surface of flanges 42 or 44, respectively, of the track 22.

Seated between the pairs of rollers 28A, 28B, and 28C, 28D is a “driven” wheel assembly 62, which serves as the assembly for driving the trolley 24. In particular, as best seen in FIGS. 3, 5, and 5A the driven wheel assembly 62 includes a left-hand located wheel 62A, a right-hand located wheel 62B and a centrally located sprocket 62C. Nested within the outside portion of the wheel 62A is a ball bearing 62D, likewise for the wheel 62B is ball bearing 62E. The wheels are constructed of polyamide, but can be formed of other suitable materials, if desired. The three components 62A, 62B and 62C are held together by conventional flat cap socket screws 62F (FIG. 5A). The driven wheel assembly is fixedly secured to an axle 70. The driven wheel assembly 62 is held in place on its associated axle by use of mechanical fixation (not shown). The axle 70 is fixedly mounted on a driven wheel support body, in the form of a weldment 140 (to be described later), by a pair of spring clips 62G. The longitudinal axis of the axle 70 extends perpendicular to the longitudinal axis of the track 22.

Since the sprocket 62C is fixedly secured between the wheels 62A and 62B, rotation of the sprocket 62C causes concomitant rotation of the wheels 62A and 62B. The driven wheel assembly 62 is driven by a drive chain 63 and drive sprocket 64. The sprocket 62C is arranged to be driven, i.e., rotated, by the drive chain 63 under the impetus of the drive sprocket 64. The drive sprocket 64 is located beneath the driven wheel assembly 62 and is also located between the pairs of rollers 28A, 28B and 28C, 28D. The drive chain 63 interlinks the sprocket 62C of the driven wheel assembly 62 and the drive sprocket 64. As best seen in FIGS. 2 and 7 the drive chain 63 is a continuous chain in the form of a loop, which extends about the drive sprocket 64 and sprocket 62C of the driven wheel assembly 62. A drive belt or other suitable loop member can be used in lieu of the chain, if desired, although the chain is preferred. When driven by the drive sprocket 64 the top portion of the periphery of the two driven wheels 62A and 62B of the driven wheel assembly 62 frictionally engage the inner surface of the top wall 32 of the track to cause the trolley to move longitudinally along the interior of the track. The drive sprocket 64 forms a portion of the tractor drive trolley 24. As should be appreciated by those skilled in the art, the positive driving of the wheels 62A and 62B minimizes the chance of wheel slippage on the inner surface of the track as may occur with the tractor of the aforementioned U.S. Pat. No. 6,718,885.

As best seen in FIG. 7 the drive sprocket 64 includes an axle 94 fixedly secured thereto and located at the center of the wheel and having end portions projecting perpendicularly outward from the sprocket and defining a rotation axis that extends perpendicularly to the longitudinal axis of the track 22. The axle 94 of the drive sprocket 64 is mounted within a pair of flanged bearings 90 on a frame portion 86 of the tractor drive trolley 24 and located outside, i.e., below, the track 22. The axle of the drive sprocket 64 is coupled via a transmission assembly including a pair of sprockets 92 and 98 and a drive belt 96 to a driving motor. In particular, the sprocket 98 is mounted on the rotary output shaft 100 of a gear reduction unit 78 which is coupled to motor 76. The motor 76 forms another portion of the tractor drive trolley 24, so that upon operation of the motor the drive sprocket 64 is rotated about an axis extending perpendicularly to the longitudinal axis of the track 22. This action causes the concomitant rotation of the driven wheel 62 about its axis, which is also perpendicular to the longitudinal axis of the track. The driven wheel 62 and the drive sprocket 64 are dimensioned so that the top portion of the periphery of the wheels 62A and 62B of the driven wheel assembly 62 frictionally engages the inner surface of the top wall 32 of the track, as shown in FIG. 2. The spring-biased rod mentioned earlier, and to be discussed later, helps ensure that the wheels 62A and 62B make good frictional engagement with the interior surface of the top wall 32 of the track. Accordingly, when the drive sprocket 64 is rotated by the motor, the driven wheel 62A and 62B is rotated in the corresponding rotational direction to frictionally engage the interior surface of the top wall 32 of the track 22 and hence push or pull (as the case may be—depending upon the direction of rotation of the driven wheels) the trolley along the track. In FIG. 2 the curved arrow represents the direction of rotation of the driven wheels 62A and 62B and drive sprocket 64 to cause the trolley to move in a forward direction along the track 22, i.e., the tractor drive pushes the trolley to the left in that figure. Rotation of the driven wheels 62A and 62B and drive sprocket 64 in the opposite directions causes the tractor drive to pull the trolley in the opposite longitudinal direction, i.e., rearward.

In order to ensure that the portions of the tractor drive that extend through the slot 46 in the track 22 into its interior, e.g., the driven wheel support body 140 (FIG. 2), do not engage or bind on the edges of the slot 46 when the trolley moves along the track, the second or rear roller section 28 includes a pair of cam rollers which act as guide rollers to center the roller sections with respect to the track. In particular as best seen in FIGS. 2 and 5, a cam roller 66 is mounted on a vertically extending bolt 68 secured to the roller support body 60 of the rear roller section 28. The axis of rotation of the cam roller 66 is vertical and centered between the peripheral edges of the flanges 42 and 44 forming the track's slot 46. The diameter of the cam roller 66 is slightly smaller than the width of the track's slot 46 so that it can be centered therein. An identical cam roller 66 is mounted on a vertically extending bolt 68 secured to the roller support body 58 of the rear roller section 28. The respective axis of rotation of each of the cam rollers 66 is vertical and centered between the peripheral edges of the flanges 42 and 44 forming the track's slot 46. Another second cam roller 67 is mounted on a vertically extending bolt 68 secured to the forward end of the driven wheel support body 140. The axis of rotation of the cam roller 67 is vertical and centered between the peripheral edges of the flanges 42 and 44 forming the track's slot 46. An identical cam roller 67 is mounted on a vertically extending bolt 68 secured to the rearward end of the driven wheel support body 140. The axis of rotation of the cam roller 67 is vertical and centered between the peripheral edges of the flanges 42 and 44 forming the track's slot 46.

The tractor drive trolley 24 basically comprises of a frame 74 (FIG. 2), the heretofore mentioned motor 76, a speed reducer 78, the heretofore mentioned transmission assembly 80, a drive wheel assembly 82 (FIG. 3) including the heretofore identified drive sprocket 64, and a spring biasing assembly 84 including the heretofore mentioned spring biased rod. The frame 74 is in the form of a weldment having an upper portion 86 supporting the drive wheel assembly 82 and driven wheel support body 140, and a lower flange 88 (FIG. 3) mounting the speed reducer 78 and a portion of the transmission assembly 80. The speed reducer is secured to the flange 88 via plural bolts and nuts. The driven wheel support body 140 is itself a weldment; having two lower legs 142, an upper body portion 144 and two mounting blocks 146 for the cam rollers 67. The two lower legs are mounted to the upper portion 86 of the frame 74 via plural bolts. The upper body portion 144 serves as the support body for the driven wheel assembly 62.

The pair of flanged bearings 90 which form a portion of the drive wheel assembly 82 are mounted on the upper portion 86 of the frame 74 and serve to journal respective portions of the axle of the drive sprocket 64. As best seen in FIG. 3, the sprocket 92 is mounted on one end portion 94 of the axle of the drive sprocket 64. As mentioned earlier the sprocket 92 forms a portion of the transmission assembly 80 that also includes a drive chain 96 and the other flanged sprocket 98. The sprocket 98 is mounted on one end of a rotary output shaft 100 of the speed reducer 78. The drive chain 96 is a continuous chain in the form of a loop, which extends about the sprockets 92 and 98. The speed reducer is a conventional device, which is connected to the rotary output shaft of the motor 76 and includes gearing to reduce its rotary output shaft's rotational speed, e.g., 1,725 rpm, to a lower rotational speed, e.g., a 40 to 1 speed reduction, and to provide that at its output shaft 100.

The rotation of the output shaft 100 of the speed reducer causes the concomitant rotation of the sprocket 98, which is coupled via the drive chain 96 to the sprocket 92 and to the axle 94 of the drive sprocket 64 to cause it to rotate at the desired speed. It should be appreciated by those skilled in the art that the number of teeth on the two sprockets could be selected to provide a different rotational speed reduction, if desired. Moreover, the motor's speed and the amount of reduction of it by the speed reducer (or by the sprockets) is a matter of choice by the designer of the system.

In order to protect the drive chain and sprockets of the transmission assembly 80, a hollow housing or cover 102 is provided on the frame 74 and extends over the sprockets and the chain. The cover 102 is held in place on the frame 74 via plural screws and lock washers 103.

As mentioned earlier it is the frictional engagement and rotation of the driven wheel 62 on the inner surface of the top wall 32 of the track, which effects the movement of the trolley 24 along the track. In order to ensure that the driven wheel makes good frictional engagement with the interior surface of the top wall 32 of the track 22 to effectively and efficiently move the trolley along the track without slippage, the heretofore spring biasing assembly 84 is provided. That assembly is mounted on the pivot plate 108. The pivot plate 108 is mounted on a vertically extending bolt 112 secured to the middle portion of the frame 74 and basically comprises the heretofore mentioned rod now designated by the reference number 104 (FIG. 2), a helical compression spring 106 and an associated pair of nuts 110 and a flat washer 109. The rod 104 is an elongated member having an upper end to which the roller supporting body 60 is fixedly secured. The upper portion of the rod 104 extends through and is journalled in a bore in the pivot plate 108 at the upper portion of the frame 74. The rod can thus rotate about its longitudinal axis in the bore. The lower portion of the rod 104 extends out the bottom of the pivot plate 108 and down through the longitudinal center of the spring 106 and out its lower end. The lower end of the rod is threaded. A flat washer 109 is mounted on the lower end of the rod 104 so that the spring 106 is interposed between it and the pivot plate 108. A pair of threaded nuts 110 is mounted on the lower threaded end of the rod to hold the washer 109 in place and to adjust the amount of compression applied to the spring 106 by the tightening of the nuts 110.

As should be appreciated by those skilled in the art, by tightening the nuts 110 on the rod 104, the spring 106 is compressed. The natural bias of the spring 106 tends to oppose this compression to thereby pull downward on the rod 104. This downward pulling of the rod 104 pulls the roller mounting body 60 and the rollers 28C and 28D mounted thereon downward. Since the rollers 28C and 28D are in engagement with the inner surfaces of the track's flanges 42 and 44, this downward pull is resisted by the flanges and is translated into an upwardly directed force on the frame 74. Accordingly, an upward force is applied through the driven wheel support body 140 to the driven wheel 62 to force it into good frictional engagement with the inner surface of the top wall 32 of the track 22. Thus, when the driven wheel 62 is driven by rotation of the drive sprocket 64, the driven wheel 62 will roll on the inner surface of the top wall 32 of the track without slippage. This results in the movement of the trolley 24 down the track at a desired speed, e.g., 50 feet per minute using the exemplary rotational speeds of the shafts as discussed above.

In order to ensure that the two roller sections 26 and 28 can readily negotiate curves in the track 22, those roller sections are coupled together by a hinged, articulated tow-arm assembly 30. To that end, as best seen in FIGS. 1 and 2, the tow-arm assembly 30 basically comprises a yoke-like tow-arm member 114, a bracket 118, and a plate-like tow-arm swing plate 116. The tow-arm swing plate 116 is fixedly secured to a mid-centrally located portion of the frame 74 as will be described later. At each end of the swing plate 116 there are two holes for securing the swing plate to a tow-arm member 114. The bracket 118 includes a flanged bushing (to be described later) and is in the form of a clevis that is secured to a portion of the plate-like member 52 of the roller support body 50 of the first or front roller section 26 (as will be described later with reference to FIG. 4). Respective pivot or hinge bolts 120 extend through respective ones of the flanged bushings making up bracket 118.

The tow-arm member 114 is a weldment having a vertical plate-like member 117 and a horizontal elongated yoke-like or U-shaped, plate member. As best seen in FIGS. 1, 6 and 7 the U-shaped plate member has a pair of parallel, longitudinally extending arms 115 straddling the frame portion 86. Located on each tip of the U-shaped member 115 are two holes used for a bolted connection to the tow-arm swing plate 116 via conventional hex bolts, lock washers and hex nuts as best seen in FIG. 6.

As best seen in FIG. 2 the vertical plate-like member 117 has a pair of linear reinforcing tabs 122 secured to the top and bottom edges of it. Each tab 122 terminates beyond the associated end of the plate-like member 117 to form a gap there between in which a respective one of the flanged bushings of the bracket 118 is located. In particular, the pivot bolt 120 of the tow-arm member closest to the plate-like member 52 of the support body 50 of the front roller section 26 extends through aligned holes in the ends of the reinforcing tabs 122 closest to the plate-like member 52. That bolt also extends through the flange bushing making up the bracket 118 and also includes a head on its upper end and a nut on its lower end to secure it to the end of the tow-arm member 114.

As best seen in FIG. 4, and as mentioned earlier, the front-end portion of the bracket 118 is in the form of a clevis having a pair of spaced apart arms 118A and 118B. The plate-like member 52 of the front roller support body 50 is located between the arms 118A and 118B of the clevis and is secured in place via a pin 126 extending through it and through the arms of the clevis. The ends of the pin 126 are held in place by any conventional means, e.g., respective cotter pins and associated flat washers 128. Thus, the front end of the tow-arm member 114 is hinged securely to the plate-like member 52 by the bolt 120 and its associated flanged bushing 118. With this arrangement, the tow-arm assembly 30 (FIG. 2) can pivot independently with respect to the frame 74 carrying the rear roller section 28 and with respect to the roller support body 50 carrying the front roller section 26.

As best seen in FIGS. 1 and 6 the tow-arm swing plate 116 is pivotably mounted on a vertically extending socket head cap screw 116A that is threaded into a boss in the frame weldment 86. The pivot joint of the tow-arm swing plate 116 is thus at this cap screw 116A which is located exactly half way between the centerlines of the fore and aft guide rollers 66 and 66 of the rear roller section and at the longitudinal position of the driven wheel 62. This arrangement distributes any lateral load, or side thrust, evenly between those guide rollers to minimize side loading and maximize guide roller durability.

As should be appreciated from the foregoing, the systems of the subject invention, and in particular their trolleys, are particularly well suited for use in any enclosed track system, even those having a relatively tight or small radius of curvature curves. The trolley 24 can be constructed in various ways and need not include all of the rollers shown and described heretofore. Moreover, other arrangements than that specifically described above can be used to effect the driving or movement of the trolley along the track by means of some motor located outside the track. Further still, this system is not limited to use with powered trolleys. Thus, the trolleys of this invention can be passive ones that are pulled along the track by hand or by some other mechanism located below the track.

While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. 

1. A trolley for use with an enclosed track having at least one curved portion, the enclosed track being an elongated hollow member having a top wall portion, a pair of side wall portions and a pair of flanged portions, the flanged portions being spaced from each other to define a slot there between extending longitudinally along the track, said trolley comprising a rolling section and a drive section, said rolling section comprising first and second roller portions, said first roller portion being located within the track and comprising at least one support roller arranged to roll on at least one of the flange portions of the track, said second roller portion comprising a driven wheel and a pair of support rollers, said drive section being located outside of the track and including a driving sprocket and an associated driving loop, said driving sprocket being arranged for positively engaging said driving loop, said driving loop being arranged for positively engaging said driven wheel to cause said driven wheel to rotate about a horizontal axis, said pair of support rollers comprising an upstream support roller and a downstream support roller, said upstream support roller being located adjacent one side of said drive wheel and mounted on said drive section for pivoting action about an upstream vertical axis, said downstream support roller being located adjacent a diametrically opposed side of said driven wheel and mounted on said drive section for pivoting action about a downstream vertical axis, whereupon said upstream and downstream support rollers are enabled to roll along at least one of the flange portions of the track while said driven wheel rolls along the top wall portion of the track in the center thereof.
 2. The trolley of claim 1 wherein said driving loop comprises a chain.
 3. The trolley of claim 1 additionally comprising at least one spring for biasing said driven wheel into engagement with the top wall of the track.
 4. The trolley of claim 1 additionally comprising a pair of guide rollers mounted on respective vertically extending rods connected to said second roller portion, each of said guide rollers being and located within the slot in the track, with said guide rollers being positioned immediately fore and aft of the position of said driven wheel.
 5. The trolley of claim 4 wherein said first roller portion is coupled to said second roller portion by an articulated joint, said articulated joint comprising an elongated member, said elongated member having a first end portion and a second end portion, said first end portion being pivotably coupled to said first roller portion at a first vertically extending axis, said second end portion being pivotably coupled to said second roller portion at a second vertically extending axis, said second vertically extending axis being located approximately midway between said vertically extending rods of said guide rollers.
 6. The trolley of claim 5 wherein said articulated joint additionally comprises a tow-arm swing plate, and wherein said elongated member is comprises a yoke like member having a pair of arms, each of which includes a respective end fixedly secured to said tow-arm swing plate, said tow-arm swing plate being mounted for pivoting about said second vertically extending axis.
 7. A trolley for use with an enclosed track having at least one curved portion, the enclosed track being an elongated hollow member having a top wall portion, a pair of side wall portions and a pair of flanged portions, the flanged portions being spaced from each other to define a slot therebetween extending longitudinally along the track, said trolley comprising a rolling section and a drive section, said rolling section comprising first and second roller portions, said first roller portion being located within the track and comprising at least one support roller arranged to roll on at least one of the flange portions of the track, said second roller portion comprising a driven wheel and a pair of support rollers, said first and second roller portions being coupled together by an articulating joint, said second roller portion comprising a pair of guide rollers mounted on respective vertically extending rods, each of said guide rollers being and located within said slot, with said guide rollers being positioned immediately fore and aft of the position of said driven wheel, said drive section being located outside of the track said driving section being arranged for driving said driven wheel to cause said driven wheel to rotate about a horizontal axis, said pair of support rollers comprising an upstream support roller and a downstream support roller, said upstream support roller being located adjacent one side of said drive wheel and mounted on said drive section for pivoting action about an upstream vertical axis, said downstream support roller being located adjacent a diametrically opposed side of said driven wheel and mounted on said drive section for pivoting action about a downstream vertical axis, whereupon said upstream and downstream support rollers are enabled to roll along at least one of the flange portions of the track while said driven wheel rolls along the top wall portion of the track in the center thereof, said articulated joint comprising an elongated member, said elongated member having a first end portion and a second end portion, said first end portion being pivotably coupled to said first roller portion at a first vertically extending axis, said second end portion being pivotably coupled to said second roller portion at a second vertically extending axis, said second vertically extending axis being located approximately midway between said vertically extending rods of said guide rollers.
 8. The trolley of claim 7 wherein said articulated joint additionally comprises a tow-arm swing plate, and wherein said elongated member is comprises a yoke like member having a pair of arms, each of which includes a respective end fixedly secured to said tow-arm swing plate, said tow-arm swing plate being mounted for pivoting about said second vertically extending axis. 